---
id: "CVE-2026-98776"
kind: "vulnerability"
aliases: ["CVE-2026-98776"]
title: "Linux kernel: binderfs race lets a concurrent unlink cause use-after-free write"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "infrastructure"
products: []
ecosystems: []
tags: ["android", "binderfs", "infrastructure", "linux-kernel"]
not_affected_if: ["binderfs-not-mounted"]
published_at: "2026-10-18T16:17:31+00:00"
first_seen_at: "2026-10-23T21:57:16+00:00"
updated_at: "2026-10-25T05:15:27+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98776", "first_seen_at": "2026-10-23T21:57:16+00:00"}]
---

# Linux kernel: binderfs race lets a concurrent unlink cause use-after-free write

In binderfs, a Binder device is published before it is fully registered, so a concurrent unlinkat() can free it while the kernel still writes to it. The sources describe a use-after-free write in binder_add_device, which can corrupt kernel memory.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `uname -r` and compare against the fixed kernel builds listed in the NVD entry.
- Check whether binderfs is mounted with `mount | grep binder`; unknown if the sources give no other check.

## Fix

- Update the Linux kernel to a release that includes the upstream binderfs fix (version unknown from the sources).
- Until patched, unload or avoid mounting binderfs where it is not needed (unknown from the sources).

## Timeline

- 2026-10-23T21:57:16+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98776

## From the sources

In the Linux kernel, the following vulnerability has been resolved:

binderfs: fix UAF write in binder_add_device

binderfs_binder_device_create() publishes the new dentry with
d_make_persistent() and then calls simple_done_creating(), which drops
the parent directory lock and the creator's dentry reference. It then
calls binder_add_device() to register the device in the global
binder_devices list.

After simple_done_creating() releases the parent directory lock, a
concurrent unlinkat() can remove the new device entry. Dropping the
creator's dentry reference can then trigger binderfs_evict_inode(),
freeing the device. binder_add_device() later accesses the freed
object, causing UAF write.

Found by a modified Syzkaller:

	BUG: KASAN: slab-use-after-free in hlist_add_head include/linux/list.h:1073 [inline]
	BUG: KASAN: slab-use-after-free in binder_add_device+0xa9/0xc0 drivers/android/binder.c:7068
	Write of size 8 at addr ffff88805b340c00 by task syz.1.532/11389

	CPU: 0 UID: 0 PID: 11389 Comm: syz.1.532 Not tainted 7.2.0 #4 PREEMPT(full)
	Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
	Call Trace:
	<TASK>
	__dump_stack lib/dump_stack.c:94 [inline]
	dump_stack_lvl+0x10e/0x1f0 lib/dump_stack.c:120
	print_address_description mm/kasan/report.c:378 [inline]
	print_report+0xf7/0x600 mm/kasan/report.c:482
	kasan_report+0xe4/0x120 mm/kasan/report.c:595
	hlist_add_head include/linux/list.h:1073 [inline]
	binder_add_device+0xa9/0xc0 drivers/android/binder.c:7068
	binderfs_binder_device_create.isra.0+0x724/0x990 drivers/android/binderfs.c:196
	binder_ctl_ioctl+0x186/0x1b0 drivers/android/binderfs.c:241
	vfs_ioctl fs/ioctl.c:51 [inline]
	__do_sys_ioctl fs/ioctl.c:597 [inline]
	__se_sys_ioctl fs/ioctl.c:583 [inline]
	__x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
	do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
	do_syscall_64+0x116/0x800 arch/x86/entry/syscall_64.c:94
	entry_SYSCALL_64_after_hwframe+0x77/0x7f
	RIP: 0033:0x7ff9027a833d
	Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
	RSP: 002b:00007ff903674018 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
	RAX: ffffffffffffffda RBX: 00007ff902a35fa0 RCX: 00007ff9027a833d
	RDX: 0000200000000500 RSI: 00000000c1086201 RDI: 0000000000000004
	RBP: 00007ff902850733 R08: 0000000000000000 R09: 0000000000000000
	R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
	R13: 00007ff902a36038 R14: 00007ff902a35fa0 R15: 00007ffd7166bfa0
	</TASK>

	Allocated by task 11389:
	kasan_save_stack+0x33/0x60 mm/kasan/common.c:57
	kasan_save_track+0x14/0x30 mm/kasan/common.c:78
	poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
	__kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:415
	kasan_kmalloc include/linux/kasan.h:263 [inline]
	__kmalloc_cache_noprof+0x2e4/0x6f0 mm/slub.c:5489
	_kmalloc_noprof include/linux/slab.h:988 [inline]
	_kzalloc_noprof include/linux/slab.h:1309 [inline]
	binderfs_binder_device_create.isra.0+0x17a/0x990 drivers/android/binderfs.c:148
	binder_ctl_ioctl+0x186/0x1b0 drivers/android/binderfs.c:241
	vfs_ioctl fs/ioctl.c:51 [inline]
	__do_sys_ioctl fs/ioctl.c:597 [inline]
	__se_sys_ioctl fs/ioctl.c:583 [inline]
	__x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
	do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
	do_syscall_64+0x116/0x800 arch/x86/entry/syscall_64.c:94
	entry_SYSCALL_64_after_hwframe+0x77/0x7f

	Freed by task 11389:
	kasan_save_stack+0x33/0x60 mm/kasan/common.c:57
	kasan_save_track+0x14/0x30 mm/kasan/common.c:78
	kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:584
	poison_slab_object mm/kasan/common.c:253 [inline]
	__kasan_slab_free+0x5f/0x80 mm/kasan/common.c:285
	kasan_slab_free include/linux/kasan.h:235 [inline]
	slab_free_hook mm/slub.c:2677 [inline]
	slab_free mm/slub.c:6377 [inline]
	kfree+0x2fc/0x6e0 mm/slub.c:6692
	binderf
---truncated---

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_